Wrong width for widget header and menu

I have been experiencing problems with my Plugins and Menus. The heading of my plugins is too short and so are the menus. You can check it out here: "http://www.4xbroker.cz".
Does anyone has the same problems?
The problems started when I instaled "customer area" plugin which uses its own stylesheet. Unfortunately this plugin is essential for me so I cannot remove it. Is there any way I could solve this?
The same trouble is causing the "WordPress Twitter Bootstrap CSS".

Luko, thanks for answering!
Actually you cannot see that problem now because I managed to remove it by modifying the padding and setting up the width to 112%.
But the problem with submenus is like its set to stone.

First I could not find the exact code as you showed. All I could find is this:

But changing these setting to what you proposed did not help. Not even pasting the code you showed.
Is it possible that there is something else that ist overwriting this code or am I just looking in the wrong place?